1. Field of the Invention
The present invention relates to a composite core to be inserted and disposed in a cavity of a casting die.
2. Description of the Related Art
Conventionally, as shown in an unexamined Japanese Patent Publication No. 07-284902, a resin core formed with a resin is known. By locating a resin core having a shape according to holes and grooves for forming a desired cast product inside a cavity of a die and by pouring molten metal into the cavity of the die to mold a cast product, even a complicated resin core can be easily removed from the cast product, without remaining core refuse in the cast product after molding, unlike the molding with such a collapsible core as a sand core.
However, holes and grooves to be formed by casting are various and large ones and small ones may be intermingled. If such a conventional collapsible core as a sand core is used, the problem in strength arises and sand cannot be discharged through a small hole. Additionally, if a resin core is used, the resin core is deformed while molten metal is poured, because of the difference of thermal capacity between a large resin core portion and a small resin core portion. This hinders the forming of high-precision casting.
An object of the invention is to provide a composite core having a resin for casting a cast product wherein a large hole and a small hole are intermingled.
According to an aspect of the present invention, a composite core for die casting comprises a large core portion for a large hole of a cast product (a casting) and a small core portion for a small hole communicating to the large hole of the cast product The large core portion includes a core base and a resin film used to coat the outer periphery of the core base, and the small core portion has a resin body formed of a resin connected to the resin film. The core base may be formed so as to be hollow.
According to another aspect of the present invention, a composite core for die casting comprises a pair of large core portions crossing each other for a pair of large holes of a cast product and a small core portion for a small hole communicating to the pair of large holes of the cast product respectively. Moreover, the pair of large core portions may include a pair of core bases and a resin film used to coat the outer periphery of the pair of core bases, and the small core portion may include a resin body formed of a resin connected to the resin film.
According to a further aspect of the present invention, a composite core used for casting a housing for a power steering on vehicle comprises a pair of large core portions crossing each other for a pair of large holes crossing each other in the housing for a contact valve and a cylinder and a small core portion for a communicating hole connected to the large holes for the contact valve and the cylinder respectively in the housing.
As aforementioned, in the composite core of the present invention, the dispersion of thermal capacity of each part is small to prevent small core portions from being deformed. Furthermore, since the core base coated with a resin is used for a large core portion, the necessary quantity of the resin is smaller than when the core is formed with only the resin. As a result, the composite core is easily formed by injection molding in a shorter time.